Motor-drive compressor

ABSTRACT

A motor-driven compressor includes a compression portion, which compresses a fluid, an electric motor, which drives the compression portion, a drive circuit, which drives the electric motor, a temperature obtaining section, which obtains the temperature of the drive circuit, and a drive mode controller, which controls the drive mode of the drive circuit. The drive mode controller controls the drive mode based on the temperature obtained by the temperature obtaining section and at least one of the rotational speed and the modulation factor of the electric motor.

BACKGROUND OF THE INVENTION

The present invention relates to a motor-driven compressor.

For example, a motor-driven compressor disclosed in Japanese Laid-Open Patent Publication No. 2005-201108 includes a compression portion, which compresses and discharges refrigerant, an electric motor, which drives the compression portion, and a drive circuit, which drives the electric motor.

Japanese Laid-Open Patent Publication No. 2011-109803 discloses the use of the pulse width modulation control (PWM control) as a method for controlling a drive circuit that drives an electric motor. In the pulse width modulation control, a control signal is generated by a voltage command signal, which specifies a voltage, and a carrier signal. Based on the control signal, ON-OFF control is executed on the switching elements in a drive circuit. Accordingly, the drive circuit converts DC power to AC power. The AC power is supplied to an electric motor to drive the motor. Further, Japanese Laid-Open Patent Publication 2011-109803 discloses, as modulation methods of the drive circuit, three-phase modulation and two-phase modulation, which are switched back and forth in accordance with the temperature of the drive circuit.

The temperature of the drive circuit may be excessively high depending on the operating condition and the environment of the drive circuit. This hampers the operation of the electric motor and the motor-driven compressor. Nevertheless, it is undesirable that an attempt to restrain an excessive increase in the temperature of the drive circuit should result, for example, in a louder noise.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide a motor-driven compressor that restrains the temperature of the drive circuit from being excessively increased in a favorable manner.

To achieve the foregoing objective and in accordance with one aspect of the present invention, a motor-driven compressor is provided that includes a compression portion, which compresses a fluid, an electric motor, which drives the compression portion, a drive circuit, which drives the electric motor and includes switching elements, a temperature obtaining section, which obtains a temperature of the drive circuit, and a drive mode controller, which controls a drive mode of the drive circuit. The drive mode includes a first drive mode, the modulation method of which is three-phase modulation, a second drive mode, the modulation method of which is two-phase modulation, and a third drive mode, which has a carrier frequency lower than a carrier frequency of the first drive mode. The modulation method of the third drive mode is three-phase modulation. The drive mode controller controls the drive mode based on a temperature obtained by the temperature obtaining section and at least one of a rotational speed and a modulation factor of the electric motor.

Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1 is a schematic diagram of a motor-driven compressor and a vehicle air conditioner;

FIG. 2 is a circuit diagram of the inverter;

FIG. 3 is an explanatory table of drive modes;

FIG. 4 is a flowchart showing a drive mode switching control process executed by the drive mode controller; and

FIG. 5 is a correlation diagram showing a manner in which the drive mode is switched.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A motor-driven compressor according to one embodiment will now be described. The motor-driven compressor of the present embodiment is mounted on a vehicle and employed in the vehicle air conditioner.

As shown in FIG. 1, the vehicle air conditioner 100 includes the motor-driven compressor 10 and an external refrigerant circuit 101, which supplies refrigerant to the motor-driven compressor 10. The external refrigerant circuit 101 includes, for example, a heat exchanger and an expansion valve. The motor-driven compressor 10 compresses refrigerant, and the external refrigerant circuit 101 performs heat exchange of the refrigerant and expands the refrigerant. This allows the vehicle air conditioner 100 to cool or warm the passenger compartment.

The vehicle air conditioner 100 includes an air conditioning ECU 102, which controls the entire vehicle air conditioner 100. The air conditioning ECU 102 is configured to obtain parameters such as the temperature of the passenger compartment and a target temperature. Based on the parameters, the air conditioning ECU 102 outputs various commands such as an ON-OFF command to the motor-driven compressor 10.

The motor-driven compressor 10 includes a housing 11, a compression portion 12, and an electric motor 13. The housing 11 has an inlet 11 a, into which refrigerant from the external refrigerant circuit 101 is drawn. The compression portion 12 and the electric motor 13 are accommodated in the housing 11.

The housing 11 is substantially cylindrical as a whole and made of a thermally conductive material (a metal such as aluminum). The housing 11 has an outlet 11 b through which refrigerant is discharged.

The compression portion 12 compresses refrigerant that has been drawn into the housing 11 through the inlet 11 a and discharges the compressed refrigerant through the outlet 11 b. The compression portion 12 may be any type such as a scroll type, a piston type, and a vane type.

The electric motor 13 drives the compression portion 12. The electric motor 13 includes a columnar rotary shaft 21, which is rotationally supported, for example, by the housing 11, a cylindrical rotor 22, which is fixed to the rotary shaft 21 and includes an embedded permanent magnet, and a stator 23 fixed to the housing 11. The axis of the rotary shaft 21 coincides with the axis of the cylindrical housing 11. The stator 23 includes a cylindrical stator core 24 and coils 25 wound about the teeth of the stator core 24. The rotor 22 and the stator 23 face each other in the radial direction of the rotary shaft 21.

As shown in FIG. 1, the motor-driven compressor 10 includes an inverter unit 30, which includes an inverter 31 and a case 32. The inverter 31 serves as a drive circuit that drives the electric motor 13, and the case 32 accommodates the inverter 31. The coils 25 of the electric motor 13 and the inverter 31 are connected to each other by connectors (not shown). The case 32 is fixed to the housing 11 with bolts 41, which serve as fasteners. That is, the inverter 31 is integrated with the motor-driven compressor 10 of the present embodiment.

The inverter 31 includes, for example, a circuit board 51 and a power module 52, which is electrically connected to the circuit board 51. The circuit board 51 has various electronic components and a wiring pattern. A temperature sensor 53 is mounted on the circuit board 51. The temperature sensor 53 serves as a temperature measuring section that measures, for example, the temperature of the circuit board 51. A connector 54 is provided on the outer surface of the case 32. The circuit board 51 and the connector 54 are electrically connected to each other. The inverter 31 receives power from a DC power source E, which serves as an external power source, via the connector 54. The air conditioning ECU 102 and the inverter 31 are electrically connected to each other.

As shown in FIG. 2, the coils 25 of the electric motor 13 are of a three-phase structure, for example, with a u-phase coil 25 u, a v-phase coil 25 v, and a w-phase coil 25 w. That is, the electric motor 13 is a three-phase motor. The coils 25 u to 25 w are connected in a Y-connection.

The power module 52 includes u-phase power switching elements Qu1, Qu2 corresponding to the u-phase coil 25 u, v-phase power switching elements Qv1, Qv2 corresponding to the v-phase coil 25 v, and w-phase power switching elements Qw1, Qw2 corresponding to the w-phase coil 25 w. That is, the inverter 31 is a three-phase inverter.

The switching elements Qu1, Qu2, Qv1, Qv2, Qw1, and Qw2 (hereinafter, simply referred to as the switching elements Qu1 to Qw2) are each constituted, for example, by an insulated gate bipolar transistor (IGBT). Each of the switching elements Qu1 to Qw2 operates normally when its temperature is lower than or equal to a predetermined operation upper limit temperature Tmax. The operation upper limit temperature Tmax is the upper limit of the guaranteed operation range of the power switching elements Qu1 to Qw2. In other words, the operation upper limit temperature Tmax is the upper limit of the guaranteed operation range of the inverter 31.

The u-phase power switching elements Qu1, Qu2 are connected to each other in series by a connection wire that is connected to the u-phase coil 25 u. The connection body of the u-phase power switching elements Qu1, Qu2 receives the DC power of the DC power source E. Except for the connected coil, the other switching elements Qv1, Qv2, Qw1, Qw2 have the same connection structure as the u-phase power switching elements Qu1, Qu2, and the descriptions thereof are omitted.

The inverter 31 includes a smoothing capacitor C1, which is connected in parallel with the DC power source E. The power module 52 includes freewheeling diodes Du1 to Dw2, which are respectively connected in parallel with the power switching elements Qu1 to Qw2.

The motor-driven compressor 10 includes a controller 55, which controls the inverter 31 (specifically, switching of the power switching elements Qu1 to Qw2). The controller 55 is connected to the gates of the power switching elements Qu1 to Qw2. The controller 55 periodically switches ON and OFF the power switching elements Qu1 to Qw2 to drive, or rotate, the electric motor 13.

The present embodiment employs a bootstrapping method to switch on the power switching elements Qu1, Qv1, Qw1 on the upper arm. Specifically, a bootstrap circuit 61, which has a capacitor 61 a, is provided between the power switching elements Qu1, Qv1, Qw1 and the controller 55. The bootstrap circuit 61 generates a voltage higher than the power source voltage, which is the voltage of the DC power source E. The controller 55 applies the voltage generated by the bootstrap circuit 61 to the gates of the power switching elements Qu1, Qv1, Qw1 on the upper arm, thereby switching on the power switching elements Qu1, Qv1, Qw1.

The controller 55 executes pulse width modulation control (PWM control) on the inverter 31. Specifically, the controller 55 uses a carrier signal and a commanded voltage value signal (signal for comparison) to generate a control signal. The controller 55 executes ON-OFF control on the power switching elements Qu1 to Qw2 by using the generated control signal, thereby converting a DC power to an AC power. The AC power obtained through the conversion is supplied to the electric motor 13 to drive the motor 13.

The controller 55 is configured to change a carrier frequency f, which is the frequency of the carrier signal. The specific waveform of the carrier signal may be any waveform such as a triangle wave or a sawtooth wave as long as the waveform allows the signal to functions as the carrier signal.

Further, the controller 55 controls the control signal to vary the duty cycle of the ON-OFF of the power switching elements Qu1 to Qw2. By varying the duty cycle, the controller 55 controls the rotational speed r of the electric motor 13. The controller 55 is electrically connected to the air conditioning ECU 102. When receiving information related to a command value for the rotational speed r (number of revolutions per unit time) from the air conditioning ECU 102, the controller 55 causes the electric motor 13 to rotate at a rotational speed r that corresponds to the command value. Hereinafter, the rotational speed r of the electric motor 13 will be simply referred to as a rotational speed r.

Further, the controller 55 controls the control signal to control a modulation factor M, which is the ratio of the amplitude of the AC voltage output by the inverter 31 to the power source voltage. The controller 55 obtains the power source voltage and a required voltage, which corresponds to a voltage required to drive the electric motor 13, and controls the modulation factor M in accordance with the power source voltage such that the output voltage of the inverter 31 becomes the required voltage.

Based on the result of measurement by the temperature sensor 53, the controller 55 obtains an inverter temperature T, which is the temperature of the inverter 31. Specifically, the temperature sensor 53 delivers the measurement result to the controller 55. The controller 55 has data related to a correlation between the measurement result of the temperature sensor 53 and the temperature of the power module 52 (specifically, the temperatures of the power switching elements Qu1 to Qw2). By referring to the data, the controller 55 derives the temperature of the power module 52, which corresponds to the measurement result of the temperature, and sets the derived temperature as the inverter temperature T. That is, the temperature sensor 53 is employed to obtain the inverter temperature T. The inverter temperature T corresponds to an obtained temperature, and the controller 55 corresponds to a temperature obtaining section.

Any temperature that relates to the inverter 31 may be used as the inverter temperature T. For example, the value measured by the temperature, that is, the temperature of the circuit board 51 may be used as the inverter temperature T.

The controller 55 includes a position obtaining section 62, which obtains the rotational position of the rotor 22. Specifically, the position obtaining section 62 estimates counter electromotive force generated in the electric motor 13 based on the voltage applied to the electric motor 13 and the current flowing through the electric motor 13. Based on the estimated counter electromotive force, the position obtaining section 62 obtains the rotational position of the rotor 22. Based on the rotational position of the rotor 22, which is obtained by the position obtaining section 62, the controller 55 executes ON-OFF control on the power switching elements Qu1 to Qw2. A structure that detects the current through the electric motor 13 may be employed. For example, a shunt resistor may be provided on the circuit board 51, and the voltage of the shunt resistor may be detected. In this case, the current is estimated based on the detected voltage.

As shown in FIG. 2, the controller 55 includes a drive mode controller 63, which controls the drive mode of the inverter 31 (hereinafter, simply referred to as the drive mode). The drive mode will now be described.

In the present embodiment, the drive mode is switched among first to third drive modes as shown in FIG. 3. In the first drive mode, the carrier frequency f is a first carrier frequency f1, and the modulation method is three-phase modulation. In the second drive mode, the carrier frequency f is a second carrier frequency f2, and the modulation method is two-phase modulation. In the third drive mode, the carrier frequency f is a third carrier frequency f3, and the modulation method is three-phase modulation.

In the present embodiment, the three-phase modulation is a drive mode in which the power switching elements Qu1 to Qw2 of all the phases are always subjected to periodic ON-OFF operation. The two-phase modulation is a drive mode in which periodic ON-OFF operation of one of the power switching elements Qu1 to Qw2, that is, the power switching element of one of the three phases, is sequentially stopped every predetermined period (phase angle). That is, the two-phase modulation is a drive mode in which the periodic ON-OFF operation of the power switching element of one of the three phases is sequentially stopped, and periodic ON-OFF operations of the power switching elements of the other two phases are executed. The state in which the periodic ON-OFF operation of a power switching element is stopped refers to a state in which the power switching element remains switched ON or OFF.

Compared to the three-phase modulation, the power switching elements Qu1 to Qw2 are less frequently switched ON and OFF. Thus, the power loss and the amount of heat generation of the inverter 31 are more likely to be increased in the three-phase modulation than in the two-phase modulation. In the description below, the power loss and the amount of heat generation refer to the power loss and the amount of heat generation of the inverter 31 unless otherwise specified.

In the two-phase modulation of the present embodiment, for example, the power switching elements Qu1, Qv1, Qw1 on the upper arm and the power switching elements Qu2, Qv2, Qw2 on the lower arm are both employed. In other words, the power switching elements Qu1 to Qw2 are each subjected to stopping.

In the present embodiment, the first carrier frequency f1 and the second carrier frequency f2 are set to be substantially the same. In contrast, the third carrier frequency f3 is set to be lower than the first carrier frequency f1. Specifically, as shown in FIG. 3, the first carrier frequency f1 and the second carrier frequency f2 are set, for example, at 20 kHz, while the third carrier frequency f3 is set, for example, at 10 kHz. The first carrier frequency f1 corresponds to the carrier frequency of the first drive mode.

As shown in FIG. 2, the controller 55 includes a field weakening controller 64, which executes field weakening control on the electric motor 13 when a predetermined field weakening condition is met. The field weakening condition, for example, refers to a state in which the counter electromotive force generated in the motor 13 is equal to the power source voltage.

The field weakening control is one of the control modes of the electric motor 13. Specifically, in the field weakening control, when the counter electromotive force is equal to the power source voltage, a current is supplied to the coils 25 u to 25 w of the stator 23 to generate a magnetic flux the direction of which is opposite to that of the magnetic flux generated by the permanent magnets embedded in the rotor 22, so that counter electromotive force is reduced.

The field weakening control is executed when the modulation method is the two-phase modulation and overmodulation control is being executed. In the overmodulation control, a power switching element that is an object to be operated is maintained in an ON state for a predetermined period longer than the carrier period. The field weakening control is executed under an environment of a relatively low power source voltage. Thus, in the field weakening control, the power loss tends to be smaller than that in the normal control.

The power switching element that is an object to be operated refers to a power switching element other than the power switching elements in a stopped phase. The following description is basically related to the normal control (in other words, non-field weakening control), unless specified as related to the field weakening control.

In the present configuration, the magnitudes of the power loss and the amount of heat generation in the normal control satisfy the expression: the first drive mode > the second drive mode > the third drive mode. Among the three drive modes, the first drive mode has the greatest amount of heat generation. At least in the normal control, the third drive mode has the smallest amount of heat generation among the three drive modes. However, since the carrier frequency f is low in the third drive mode, the third drive mode tends to generate louder noise.

At the start of operation of the motor-driven compressor (specifically, the electric motor 13), the drive mode controller 63 sets the drive mode to the first drive mode. That is, the first drive mode is an initial drive mode in the present embodiment. The drive mode controller 63 is configured to obtain the current drive mode.

Thereafter, during operation of the motor-driven compressor 10 (during operation of the electric motor 13), the drive mode controller 63 periodically executes a drive mode switching control process for switching the drive mode based on the rotational speed r and the modulation factor M of the electric motor 13 and the inverter temperature T. The drive mode switching control process will now be described.

As shown in FIG. 4, the drive mode controller 63 determines at step S101 whether the current drive mode is the first drive mode. When determining that the current drive mode is not the first drive mode, the drive mode controller 63 proceeds to step S106. In contrast, when the current drive mode is the first drive mode, the drive mode controller 63 proceeds to step S102 and determines whether a condition for shifting to the second drive mode is met. Specifically, at step S102, the drive mode controller 63 determines whether a predetermined two-phase modulation condition is met.

The two-phase modulation condition is determined based on the restrictions on the inverter 31. In the present embodiment, the two-phase modulation condition is defined by at least one of the rotational speed r and modulation factor M. Specifically, the two-phase modulation condition is met when the rotational speed r is greater than or equal to a predetermined threshold rotational speed rth and the modulation factor M is greater than or equal to a predetermined threshold modulation factor Mth.

The threshold rotational speed rth may be any predetermined value, which is, for example, determined based on the capacitance of the capacitor 61 a of the bootstrap circuit 61. Specifically, in the two-phase modulation, which uses both of the upper arm and the lower arm, any of the power switching elements Qu1, Qv1, Qw1 on the upper arm needs to be maintained ON for a specific period (for example, a period of 60 degrees of the electrical angle). The lower the rotational speed r, the longer the specific period becomes. In contrast, a maintenance enabled period, in which the power switching elements Qu1, Qv1, Qw1 can be maintained ON, depends on the capacitance of the capacitor 61 a. In this case, the specific period may be longer than the maintenance enabled period depending on the combination of the capacitance of the capacitor 61 a and the rotational speed r. Thus, the threshold rotational speed rth is set to a value at which the specific period, which corresponds to the threshold rotational speed rth, is equal to or slightly shorter than the maintenance enabled period.

The threshold modulation factor Mth may be any predetermined value, which is, for example, determined based on the specifications of the power switching elements Qu1 to Qw2 (for example, the delay time).

When the two-phase modulation condition is met, that is, when the rotational speed r is greater than or equal to threshold rotational speed rth and the modulation factor M is greater than or equal to the threshold modulation factor Mth, the drive mode controller 63 proceeds to step S103. At step S103, the drive mode controller 63 shifts the drive mode from the first drive mode to the second drive mode and ends the drive mode switching control process.

In contrast, the two-phase modulation condition is not met, that is, when the rotational speed r is less than the threshold rotational speed rth or the modulation factor M is less than the threshold modulation factor Mth, the drive mode controller 63 makes a negative determination at step S102 and proceeds to step S104. At step S104, the drive mode controller 63 determines whether a condition for shifting to the third drive mode is met. Specifically, the drive mode controller 63 obtains the inverter temperature T from the measurement result of the temperature sensor 53 and determines whether the inverter temperature T is higher than a predetermined primary third drive mode initiating temperature Tu1. The primary third drive mode initiating temperature Tu1 is lower than the operation upper limit temperature Tmax and is set, for example, at 70° C.

When the inverter temperature T is lower than or equal to the primary third drive mode initiating temperature Tu1, the drive mode controller 63 ends the drive mode switching control process without further processing. In contrast, when the inverter temperature T is higher than the primary third drive mode initiating temperature Tu1, the drive mode controller 63 switches the drive mode from the first drive mode to the third drive mode at step S105 and ends the drive mode switching control process.

In the present embodiment, the drive mode controller 63 executes step S102 before executing step S104. Thus, in a situation in which the drive mode is the first drive mode, the condition for shifting to the second drive mode (two-phase modulation condition) and the condition for shifting to the third drive mode (T>Tu1) are both met, the drive mode controller 63 prioritizes shifting to the second drive mode over shifting to the third drive mode.

As shown in FIG. 4, the drive mode controller 63 determines at step S106 whether the current drive mode is the second drive mode. When determining that the current drive mode is not the second drive mode, the drive mode controller 63 proceeds to step S111. In contrast, when the current drive mode is the second drive mode, the drive mode controller 63 proceeds to step S107 and determines whether the condition for shifting to the third drive mode is met. Specifically, the drive mode controller 63 determines whether the inverter temperature T is higher than a predetermined secondary third drive mode initiating temperature Tu2 and a controlling process other than the field weakening control is being executed. In other words, the drive mode controller 63 determines whether the inverter temperature T is higher than the predetermined secondary third drive mode initiating temperature Tu2, the normal control is being executed, and the field weakening control is not being executed. The secondary third drive mode initiating temperature Tu2 is in a range lower than the operation upper limit temperature Tmax and is higher than the primary third drive mode initiating temperature Tu1 (TMax>Tu2>Tu1). The secondary third drive mode initiating temperature Tu2 is set, for example, at 90° C.

When the inverter temperature T is higher than the secondary third drive mode initiating temperature Tu2, and a controlling process other than the field weakening control is being executed (that is, the normal control is being executed), the drive mode controller 63 proceeds to step S108, at which the drive mode controller 63 shifts the drive mode from the second drive mode to the third drive and ends the drive mode switching control process.

When the inverter temperature T is lower than or equal to the secondary third drive mode initiating temperature Tu2 or when the field weakening control is being executed, the drive mode controller 63 makes a negative determination at step S107 and proceeds to step S109 to determine whether a condition for shifting to the first drive mode is met. Specifically, at step S109, the drive mode controller 63 determines whether the two-phase modulation condition is not met. When the two-phase modulation condition is met, the drive mode controller 63 makes a positive determination at step S109 and ends the drive mode switching control process without further processing. In contrast, when the two-phase modulation condition is not met, the drive mode controller 63 makes a negative determination at step S109 and proceeds to step S110. At step S110, the drive mode controller 63 shifts the drive mode from the second drive mode to the first drive mode and ends the drive mode switching control process. That is, in a situation in which the drive mode is the second drive mode, the drive mode controller 63 shifts the drive mode from the second drive mode to the first drive mode based on the fact that the two-phase modulation condition is no longer met.

When the current drive mode is neither the first drive mode nor the second drive mode (step S101: NO, step S106: NO), the current drive mode is the third drive mode. In this case, the drive mode controller 63 determines whether a condition for shifting to the second drive mode is met at step S111. Specifically, the drive mode controller 63 determines at step S111 whether the inverter temperature T is lower than a predetermined second drive mode initiating temperature Td2 and the two-phase modulation condition is met. The second drive mode initiating temperature Td2 is lower than the secondary third drive mode initiating temperature Tu2 and is, for example, 85° C.

When the inverter temperature T is lower than the second drive mode initiating temperature Td2 and the two-phase modulation condition is met, the drive mode controller 63 shifts the drive mode from the third drive mode to the second drive mode at step S112 and ends the drive mode switching control process.

In contrast, when the inverter temperature T is higher than or equal to the second drive mode initiating temperature Td2 or when the two-phase modulation condition is not met, the drive mode controller 63 makes a negative determination at step S111 and proceeds to step S113 to determine whether a condition for shifting to the first drive mode is met. Specifically, the drive mode controller 63 determines at step S113 whether the inverter temperature T is lower than a predetermined first drive mode initiating temperature Td1. The first drive mode initiating temperature Td1 is lower than the primary third drive mode initiating temperature Tu1 and the second drive mode initiating temperature Td2. For example, the first drive mode initiating temperature Td1 is, for example, 65° C.

When the inverter temperature T is higher than or equal to the first drive mode initiating temperature Td1, the drive mode controller 63 ends the drive mode switching control process without further processing. In contrast, when the inverter temperature T is lower than the first drive mode initiating temperature Td1, the drive mode controller 63 switches the drive mode from the third drive mode to the first drive mode at step S114 and ends the drive mode switching control process.

In the present embodiment, the primary third drive mode initiating temperature Tu1 and the first drive mode initiating temperature Td1 are determined such that, within the guaranteed operation range of the power switching elements Qu1 to Qw2, the temperature range that permits operation in the first drive mode is wider than the temperature range that permits operation in the third drive mode. The secondary third drive mode initiating temperature Tu2 and the second drive mode initiating temperature Td2 are determined such that, within the guaranteed operation range of the power switching elements Qu1 to Qw2, the temperature range that permits operation in the second drive mode is wider than the temperature range that permits operation in the third drive mode.

Operation of the present embodiment will now be described with reference to FIG. 5.

When the inverter temperature T is relatively low (T≦Tu1), the drive mode is set to the first drive mode or the second drive mode depending on whether or not the two-phase modulation condition is met as shown in FIG. 5.

When the two-phase modulation condition is not met, the drive mode is set to the first drive mode or the third drive mode in accordance with the inverter temperature T. In contrast, when the two-phase modulation condition is met, the drive mode is set to the second drive mode or the third drive mode in accordance with the inverter temperature T and the control mode of the electric motor 13 (whether the field weakening control is being executed).

The present embodiment, which has been described, has the following advantages.

(1) The motor-driven compressor 10 includes the compression portion 12, which compresses refrigerant serving as fluid, the electric motor 13, which drives the compression portion 12, the inverter 31, which is a drive circuit configured to drive the electric motor 13, and the controller 55, which obtains the inverter temperature T, or the temperature of the inverter 31, and controls the inverter 31. The controller 55 includes the drive mode controller 63, which controls the drive mode of the inverter 31.

The drive mode is switched among the first drive mode, the second drive mode, and the third drive mode. In the first drive mode, the carrier frequency f is a first carrier frequency f1, and the modulation method is three-phase modulation. In the second drive mode, the carrier frequency f is the second carrier frequency f2, which is equal to the first carrier frequency f1, and the modulation method is the two-phase modulation. In the third drive mode, the carrier frequency f is the third carrier frequency f3, which is lower than the first carrier frequency f1, and the modulation method is the three-phase modulation. The drive mode controller 63 controls the drive mode based on the rotational speed r and the modulation factor M of the electric motor 13 and the inverter temperature T. Accordingly, the inverter 31 is driven in the drive mode optimal for the situation, so that the inverter temperature T is reliably restrained from being excessively high.

Specifically, the drive mode includes the first drive mode and the second drive mode. The first drive mode employs the three-phase modulation and is versatile. In contrast, the second drive mode employs the two-phase modulation. Since the two-phase modulation tends to reduce the power loss compared to the three-phase modulation, the two-phase modulation tends to generate less heat. However, to set the modulation method to the two-phase modulation, a certain condition, which is specified, for example, by the rotation speed r, (two-phase modulation condition) needs to be met. Thus, for example, depending on the rotational speed r, the drive mode cannot be shifted to the second drive mode and is maintained at the first drive mode for an extended period of time. As a result, the inverter temperature T may be increased excessively, for example, to a temperature higher than the operation upper limit temperature Tmax.

In this regard, the present embodiment has the third drive mode, which is different from the first drive mode and the second drive mode. In the third drive mode, the carrier frequency f is set to be lower than the first carrier frequency f1, and the amount of heat generation is likely to be smaller than that in the first drive mode. Since the modulation method of the third drive mode is the three-phase modulation, the third drive mode can be set regardless of conditions such as the rotational speed r. Thus, for example, when the inverter temperature T is relatively high, the drive mode is shifted from the first drive mode to the third drive mode to limit the increase in the inverter temperature T.

To limit the power loss, the drive mode may always be set at the third drive mode. However, since the carrier frequency f is low in the third drive mode, the noise would be easily increased. In contrast, the present embodiment switches the drive mode to any of the first to third drive modes in accordance with the situation, so that reduction of noise and limitation of the increase in the inverter temperature T are both achieved. Thus, the inverter 31 is permitted to operate in a range in which the inverter temperature T is not excessively increased.

(2) In a situation in which the drive mode is the first drive mode, the drive mode controller 63 shifts the drive mode from the first drive mode to the second drive mode based on the fact that the two-phase modulation condition, which is defined by both of the rotational speed r and the modulation factor M, is met. In a situation in which the drive mode is the first drive mode, the drive mode controller 63 shifts the drive mode from the first drive mode to the third drive mode based on the fact that the inverter temperature T exceeds the predetermined primary third drive mode initiating temperature Tu1. Thus, when the two-phase modulation condition is met, the drive mode is shifted from the first drive mode to the second drive mode to reduce the power loss and the amount of heat generation. When the inverter temperature T exceeds the primary third drive mode initiating temperature Tu1, the drive mode is shifted from the first drive mode to the third drive mode to reduce the power loss and the amount of heat generation. This limits the noise and restrains the inverter temperature T from being excessively high.

Particularly, the primary third drive mode initiating temperature Tu1 is set to be lower than the operation upper limit temperature Tmax of the power switching elements Qu1 to Qw2. Thus, the drive mode is shifted to the third drive mode before the operation of the power switching elements Qu1 to Qw2 is hampered, and the inverter temperature T is restrained from reaching the operation upper limit temperature Tmax.

(3) In a situation in which the drive mode is the first drive mode, the drive mode controller 63 shifts the drive mode from the first drive mode to the second drive mode when the two-phase modulation condition is met and the inverter temperature T is higher than the primary third drive mode initiating temperature Tu1. In this configuration, when the condition for shifting to the second drive mode and the condition for shifting to the third drive mode are both met, the drive mode is shifted the second drive mode with priority. In the second drive mode, the amount of heat generation and the noise are more likely to be reduced than in the first drive mode. Since the drive mode is shifted to the second drive mode with priority, the noise and the increase in the inverter temperature T are both limited.

(4) In a situation in which the drive mode is the second drive mode, the drive mode controller 63 shifts the drive mode from the second drive mode to the third drive mode based on the fact that the predetermined third drive mode shifting condition is met. The third drive mode shifting condition includes the inverter temperature T being higher than the secondary third drive mode initiating temperature Tu2, which is set to be higher than the primary third drive mode initiating temperature Tu1.

In this configuration, the secondary third drive mode initiating temperature Tu2, which is used as the condition for switching the second drive mode to the third drive mode, is higher than the primary third drive mode initiating temperature Tu1, which is used as the condition for switching the first drive mode to the third drive mode. Thus, in the first drive mode, in which the amount of heat generation is more likely to be increased than in the second drive mode, the drive mode is shifted to the third drive mode at a relatively early stage, so that the increase in the inverter temperature T is dealt with at an early stage. In contrast, in the second drive mode, in which the amount of heat generation is more likely to be reduced than in the first drive mode, the second drive mode is maintained for a relatively long period of time. This allows the noise to be reduced.

(5) The controller 55 includes the field weakening controller 64, which executes field weakening control on the electric motor 13 when the predetermined field weakening condition is met. Thus, for example, even in a condition in which the rotational speed r is relatively high and the power source voltage is relatively low, the execution of the field weakening control allows the required voltage, which corresponds to a voltage required to drive the electric motor 13, to be supplied to the electric motor 13.

The field weakening control tends to generate small amount of heat compared to the normal control. Thus, when the drive mode is the second drive mode and the field weakening control is being executed, the amount of heat generation may be substantially equal to or slightly less than that in the third drive mode. In this regard, in the present embodiment, even if the drive mode is the second drive mode, and the inverter temperature T is higher than the secondary third drive mode initiating temperature Tu2, the second drive mode is not shifted to the third drive mode as long as the field weakening control is being executed. Accordingly, unnecessary shifting of the drive mode is restrained.

(6) In a situation in which the drive mode is the third drive mode, the drive mode controller 63 shifts the drive mode from the third drive mode to the first drive mode based on the fact that the inverter temperature T is lower than the first drive mode initiating temperature Td1. Also, in a situation in which the drive mode is the third drive mode, the drive mode controller 63 shifts the drive mode from the third drive mode to the second drive mode based on the fact that the inverter temperature T is lower than the second drive mode initiating temperature Td2 and the two-phase modulation condition is met. This allows the drive mode to be shifted from the third drive mode to the second drive mode without going through the first drive mode.

The first drive mode initiating temperature Td1 is set to be lower than the second drive mode initiating temperature Td2. Accordingly, the drive mode is shifted to the first drive mode, in which the amount of heat generation is relatively great, when the inverter temperature T has sufficiently dropped. Thus, the inverter temperature T is restrained from being increased. On the other hand, the drive mode is shifted to the second drive mode, in which the amount of heat generation is relatively small, at a relatively early stage. This allows the noise to be reduced.

(7) The first drive mode initiating temperature Td1 is lower than the primary third drive mode initiating temperature Tu1, and the second drive mode initiating temperature Td2 is lower than the secondary third drive mode initiating temperature Tu2. Thus, the drive mode is restrained from being shifted from the first drive mode to the third drive mode immediately after being shifted from the third drive mode to the first drive mode.

The above embodiment may be modified as follows.

During rotation of the electric motor 13, the controller 55 may stop the electric motor 13 based on the fact that the inverter temperature T reaches a predetermined stop initiating temperature. In this case, the stop initiating temperature is preferably equal to the operation upper limit temperature Tmax or lower than the operation upper limit temperature Tmax by a certain margin, for example.

In this configuration, the third drive mode initiating temperatures Tu1, Tu2 are preferably lower than the stop initiating temperature. Thus, the drive mode is shifted to the third drive mode before the electric motor 13 is stopped. This prevents the electric motor 13 from being stopped or extends the period before the electric motor 13 is stopped. Therefore, inconvenience caused by stopping of the electric motor 13, for example, discomfort experienced by the driver due to stopping of the operation of the vehicle air conditioner 100 is limited.

The first carrier frequency f1 and the third carrier frequency f3 may have any values as long as the third carrier frequency f3 is lower than the first carrier frequency f1.

In the illustrated embodiment, the second carrier frequency f2 is equal to the first carrier frequency f1, but may be lower than or higher than the first carrier frequency f1. That is, the second carrier frequency f2 may be set to any value as long as the amount of heat generation of the second mode is smaller than that of the first drive mode during the normal control (non-field weakening control) and the noise in the third drive mode is lower than that in the normal control (non-field weakening control). In other words, the second drive mode may be modified as long as, even if the modification method is the two-phase modulation, the amount of heat generation at least during the normal control is smaller than that in the first drive mode, and the noise is lower than in the third drive mode.

Each of the drive mode initiating temperatures Tu1, Tu2, Td1, Td2 is not limited to the temperature in the above illustrated embodiment, but may be any temperature as long as it is lower than or equal to the operation upper limit temperature Tmax. For example, the third drive mode initiating temperatures Tu1, Tu2 may be the same value. Also, the first drive mode initiating temperature Td1 and the second drive mode initiating temperature Td2 may be the same value. Further, the primary third drive mode initiating temperature Tu1 and the first drive mode initiating temperature Td1 may be the same value.

In the illustrated embodiment, the two-phase modulation condition is defined by both of the rotational speed r and the modulation factor M, but may be defined by only one of these. For example, in a configuration in which the power switching elements Qu1, Qv1, Qw1 on the upper arm are switched on by a method that does not use the bootstrap circuit 61, the condition related to the rotational speed r may be omitted. Also, if the minimum duty cycle that is achievable by the inverter 31 is sufficiently low, the condition related to the modulation factor M may be omitted. That is, the two-phase modulation condition may be defined by at least one of the rotational speed r and the modulation factor M. In other words, the drive mode controller 63 may control the drive mode based on the inverter temperature T and at least one of the rotational speed r and the modulation factor M.

The drive mode may be directly shifted from the third drive mode to the second drive mode. Even in this case, the drive mode is shifted from the third drive mode to the second drive mode via the first drive mode. However, this modification involves unnecessary shifting of the drive mode and does not allow the drive mode to be shifted unless the inverter temperature T drops below the first drive mode initiating temperature Td1, which is lower than the second drive mode initiating temperature Td2. Thus, the drive mode is preferably directly shifted from the third drive mode to the second drive mode.

In a situation in which the drive mode is the first drive mode, if the condition for shifting to the second drive mode and the condition for shifting to the third drive mode are both met, the drive mode may be shifted to the third drive mode with priority.

The field weakening controller 64 may be omitted. That is, the field weakening control does not need to be executed.

The case 32 may be attached to any position on the housing 11.

The two-phase modulation is not limited to the method that uses both of the upper arm and the lower arm, but may be a method that uses only the lower arm. In other words, the two-phase modulation may stop operation of only the power switching elements Qu2, Qv2, Qw2 of the lower arm.

The motor-driven compressor 10 may be mounted on any structure other than a vehicle.

In the illustrated embodiment, the motor-driven compressor 10 is used in the vehicle air conditioner 100, but may be used in any other device. For example, if the vehicle is a fuel cell vehicle (FCV), which mounts a fuel cell, the motor-driven compressor 10 may be used in a supplying device that supplies air to the fuel cell. That is, the fluid to be compressed may be any fluid such as refrigerant or air. 

1. A motor-driven compressor comprising: a compression portion, which compresses a fluid; an electric motor, which drives the compression portion; a drive circuit, which drives the electric motor and includes switching elements; a temperature obtaining section, which obtains a temperature of the drive circuit; and a drive mode controller, which controls a drive mode of the drive circuit, wherein the drive mode includes a first drive mode, the modulation method of which is three-phase modulation, a second drive mode, the modulation method of which is two-phase modulation, and a third drive mode, which has a carrier frequency lower than a carrier frequency of the first drive mode, the modulation method of the third drive mode being three-phase modulation, and the drive mode controller controls the drive mode based on a temperature obtained by the temperature obtaining section and at least one of a rotational speed and a modulation factor of the electric motor.
 2. The motor-driven compressor according to claim 1, wherein in a situation in which the drive mode is the first drive mode, the drive mode controller shifts the drive mode from the first drive mode to the second drive mode based on the fact that a two-phase modulation condition, which is defined by at least one of the rotational speed and modulation factor, is met, and in a situation in which the drive mode is the first drive mode, the drive mode controller shifts the drive mode from the first drive mode to the third drive mode based on the fact that the obtained temperature is higher than a predetermined third drive mode initiating temperature.
 3. The motor-driven compressor according to claim 2, wherein the third drive mode initiating temperature is a primary third drive mode initiating temperature, in a situation in which the drive mode is the second drive mode, the drive mode controller shifts the drive mode from the second drive mode to the third drive mode based on the fact that a predetermined third drive mode shifting condition is met, the third drive mode shifting condition includes the obtained temperature being higher than a predetermined secondary third drive mode initiating temperature, and the secondary third drive mode initiating temperature is higher than the primary third drive mode initiating temperature.
 4. The motor-driven compressor according to claim 3, further comprising a field weakening controller, which executes field weakening control on the electric motor when a predetermined field weakening condition is met, and the third drive mode shifting condition is met when the obtained temperature is higher than the secondary third drive mode initiating temperature and the field weakening controller is not executing the field weakening control.
 5. The motor-driven compressor according to claim 3, wherein in a situation in which the drive mode is the third drive mode, the drive mode controller shifts the drive mode from the third drive mode to the first drive mode based on the fact that the obtained temperature is lower than a predetermined first drive mode initiating temperature, in a situation in which the drive mode is the third drive mode, the drive mode controller shifts the drive mode from the third drive mode to the second drive mode based on the fact that the obtained temperature is lower than a predetermined second drive mode initiating temperature and the two-phase modulation condition is met, and the first drive mode initiating temperature is lower than the second drive mode initiating temperature.
 6. The motor-driven compressor according to claim 2, wherein, in a situation in which the drive mode is the first drive mode, the drive mode controller shifts the drive mode from the first drive mode to the second drive mode when the two-phase modulation condition is met and the obtained temperature is higher than the third drive mode initiating temperature.
 7. The motor-driven compressor according to claim 1, wherein the electric motor is a three-phase motor, and the drive circuit is a three-phase inverter. 